
class OpenManager {
  // 工厂模式
  factory OpenManager() =>_getInstance();
  static OpenManager get instance => _getInstance();
  static OpenManager _instance;
  OpenManager._internal() {
    // 初始化
  }
  static OpenManager _getInstance() {
    if (_instance == null) {
      _instance = new OpenManager._internal();
    }
    return _instance;
  }
}